1. Field of the Invention
The present invention relates to an apparatus for bending a glass sheet, and more particularly to an apparatus for bending a laminated glass sheet and reinforced glass sheet which will be used as window glass sheets for automobiles.
2. Description of the Relevant Art
One method for bending laminated glass sheets which will be used as automotive window glass sheets is known as a gravity bending method. According to the gravity bending method, two glass sheets are placed one on the other and bent or shaped by gravity. However, the gravity bending method has limitations as it is unable satisfactorily to shape modern automotive window glass sheets which have relatively complex and deeply curved configurations. Specifically, since the weight of glass sheets is imposed substantially uniformly over the entire surfaces thereof during the process of the gravity bending method, it is necessary to control the temperature distribution over the glass sheets accurately while bending them to a complex shape. It is however difficult and costly to control the temperature distribution over glass sheets with the presently available gravity bending technology.
Various glass sheet bending apparatus are disclosed in:
1. U.S. Pat. No. 4,290,796 patented Sept. 22, 1981;
2. Japanese Laid-Open Patent Publication No. 57-140325 published Aug. 30, 1982; and
3. U.S. Pat. No. 4,738,704 patented Apr. 19, 1988.
Apparatus for pressing a glass sheet to shape between a pair of molds without gravity bending are disclosed in:
4. U.S. Pat. No. 3,338,695 patented Aug. 29, 1967;
5. Japanese Laid-Open Utility Model Publication No. 62-129033 published Aug. 15, 1987; and
6. Japanese Laid-Open Patent Publication No. 62-270429 published Nov. 24, 1987.
According to the glass sheet bending apparatus disclosed in the publications Nos. 1 and 2 above, a lower mold carrying a glass sheet is conveyed into a heating furnace in which the glass sheet is bent by gravity and then pressed to shape by an upper mold near the exit of the heating furnace. While the glass sheet is being bent by gravity, the glass sheet tends to sag into an undesirable configuration just like the bottom of a cooking pan, for example. The glass sheet configuration thus produced cannot easily be corrected when the glass sheet is later pressed between the upper and lower molds.
The apparatus disclosed in the publication No. 3 above operates as follows: First, a glass sheet is fed into a position below an upper mold in a heating furnace, and then bent to shape by applying a hot air flow under pressure to press the glass sheet against the lower surface of the upper mold. Thereafter, the pressure of the hot air flow is lowered, and the glass sheet is attracted to the upper mold under a vacuum. According to this apparatus, the glass sheet is pressed to shape under the uniform and moderate pressure of the hot air flow. Therefore, it is difficult to bend the glass sheet into a deep and/or complex configuration.
In the apparatus shown in the publication No. 4, the upper edge of a glass sheet is gripped and suspended by tongues when it is shaped with heat. The tongues leave their marks on the upper edge of the glass sheet.
The apparatus shown in the publication No. 5 has feed rolls for feeding a glass sheet, which extend in a direction across a concave mold through respective pockets defined in the concave mold. Consequently, only a partial region of the concave mold is used to press the glass sheet to shape. If the entire region of the concave mold were employed to press the glass sheet, then the shaped glass sheet would have marks of the pockets.
In the apparatus disclosed in the publication No. 6, a glass sheet which has been fed in a horizontal condition is attracted to a convex mold under a vacuum, and is then pressed by a lower mold positioned below the glass sheet. Since the glass sheet is attracted to the convex mold against gravity, a strong vacuum must be applied to attract the glass sheet against the convex mold. The forced attraction of the glass sheet to the convex mold prior to the shaping of the glass sheet tends to cause the heat insulating cloth on the convex mold to leave its mark on the glass sheet, and also makes it difficult to separate the shaped glass sheet easily from the convex mold. If the glass sheet were not attracted positionally accurately to the convex mold, the glass sheet would not be shaped accurately to a desired configuration.
The present invention has been made in an effort to solve the various problems, as described above, of the conventional glass sheet bending apparatus.